The manipulation of river ecosystems through dam construction or other changes transforms their natural state into a reservoir and causes aquatic animals to face new ecological and evolutionary challenges. This study was conducted to survey the impacts of Tarik dam on the body shape of two isolated populations of riffle minnows using the geometric morphometric method. Thirty specimens were captured from each side of Tarik dam. The left side of each specimen was photographed using a digital camera, and eighteen landmark points were digitized on two-dimensional images using TpsDig2. After GPA, landmark data were analyzed using DFA and TtestHotelling and the patterns of body shape differences between two populations were illustrated on a wireframegraph. The Results revealed significant differences between the body shape of the two studied populations (P<0.0001).Body shape differences between the two populations were related to head, snout, anal fin and caudal peduncle regions. These findings suggest that the characteristics of a new reservoir along with geographical separation act as evolutionary factors bringing about change to the morphological attributes of the fish inhabiting these areas